1. Field of the Invention
The present invention relates to a combined torque motor and rotary flow control valve unit which is adapted to control a flow of a fluid through a fluid channel in response to electric signals.
2. Description of the Related Art
A combined torque motor and flow control valve unit has previously been proposed in which a torque motor and a rotary flow control valve are incorporated within a common housing (e.g., Japanese Unexamined Patent Publication (Kokai) No. 60-180466). The torque motor includes a stationary electromagnet and an oscillatable rotor which is made from a permanent magnet and is magnetically biased in one direction or the other according to the polarities of the electromagnet. The rotary flow control valve includes a rotary flow control member which is fitted with clearance within a bore of the housing. A common shaft rotatably supported by the housing is disposed between the torque motor and the flow control valve. An end of the shaft is connected to the rotor of the torque motor and the other end of the shaft connected to the rotary flow control member to couple the rotor and the flow control member with each other in a torque transmitting relationship.
The problem which must be overcome in the design of a combined torque motor and rotary valve unit where high hydraulic pressures are encountered is to provide an adequate sealing means which will prevent fluid leakage through the clearance between the rotary flow control member and the bore in the housing into the component parts of the torque motor. It has often been necessary to provide an O-ring which is disposed under a very high sealing pressure between the housing and the rotatable shaft in order to prevent fluid leakage around the shaft. The sealing pressures have been high enough to inhibit the oscillating movement of the shaft. The rotatable shaft is subjected to high frictional forces which, in turn, considerably increase the loads to be imposed on the torque motor. To overcome the frictional forces, a large high output torque motor has been required.